D'Amato Anthony W, Orwig David A, Foster David R
Department of Forest Resources, University of Minnesota, St. Paul, Minnesota 55108, USA.
Ecol Appl. 2008 Jul;18(5):1182-99. doi: 10.1890/07-0919.1.
Old-growth forests are valuable sources of ecological, conservation, and management information, yet these ecosystems have received little study in New England, due in large part to their regional scarcity. To increase our understanding of the structures and processes common in these rare forests, we studied the abundance of downed coarse woody debris (CWD) and snags and live-tree size-class distributions in 16 old-growth hemlock forests in western Massachusetts. Old-growth stands were compared with eight adjacent second-growth hemlock forests to gain a better understanding of the structural differences between these two classes of forests resulting from contrasting histories. In addition, we used stand-level dendroecological reconstructions to investigate the linkages between disturbance history and old-growth forest structure using an information-theoretic model selection framework. Old-growth stands exhibit a much higher degree of structural complexity than second-growth forests. In particular, old-growth stands had larger overstory trees and greater volumes of downed coarse woody debris (135.2 vs. 33.2 m3/ha) and snags (21.2 vs. 10.7 m3/ha). Second-growth stands were characterized by either skewed unimodal or reverse-J shaped diameter distributions, while old-growth forests contained bell-shaped, skewed unimodal, rotated sigmoid, and reverse J-shaped distributions. The variation in structural attributes among old-growth stands, particularly the abundance of downed CWD, was closely related to disturbance history. In particular, old-growth stands experiencing moderate levels of canopy disturbance during the last century (1930s and 1980s) had greater accumulations of CWD, highlighting the importance of gap-scale disturbances in shaping the long-term development and structural characteristics of old-growth forests. These findings are important for the development of natural disturbance-based silvicultural systems that may be used to restore important forest characteristics lacking in New England second-growth stands by integrating structural legacies of disturbance (e.g., downed CWD) and resultant tree-size distribution patterns. This silvicultural approach would emulate the often episodic nature of CWD recruitment within old-growth forests.
原始森林是生态、保护和管理信息的宝贵来源，但由于其在新英格兰地区较为稀少，这些生态系统在该地区很少受到研究。为了增进我们对这些稀有森林中常见结构和过程的理解，我们研究了马萨诸塞州西部16片原始铁杉林中倒下的粗木质残体（CWD）的数量、枯立木以及活树的径级分布。将原始林分与八片相邻的次生铁杉林进行比较，以便更好地理解这两类森林由于不同历史而产生的结构差异。此外，我们使用林分水平的树木年轮生态学重建方法，通过信息论模型选择框架来研究干扰历史与原始森林结构之间的联系。原始林分比次生林表现出更高程度的结构复杂性。特别是，原始林分有更高大的上层树木，倒下的粗木质残体（135.2立方米/公顷对33.2立方米/公顷）和枯立木（21.2立方米/公顷对10.7立方米/公顷）的体积更大。次生林分的特征是直径分布呈偏态单峰或反J形，而原始森林包含钟形、偏态单峰、旋转S形和反J形分布。原始林分之间结构属性的变化，特别是倒下的CWD的数量，与干扰历史密切相关。特别是，在上个世纪（20世纪30年代和80年代）经历中等程度林冠干扰的原始林分有更多的CWD积累，这突出了林窗尺度干扰在塑造原始森林长期发展和结构特征方面的重要性。这些发现对于基于自然干扰的营林系统的发展很重要，该系统可用于通过整合干扰的结构遗产（如倒下的CWD）和由此产生的树木大小分布模式，恢复新英格兰次生林分中缺乏的重要森林特征。这种营林方法将模拟原始森林中CWD补充通常的间歇性特点。
